Messenger seems to be React Native evident by RCTView everywhere. It also uses NSView instead of UIView.
WhatsApp seems to use UIView, but I couldn't find evidence of SwiftUI, so am assuming its just a UIKit app.
There are some very similar UI components to the mobile app, so I am guessing they want to unify as much as they can between the two codebases.
WhatsApp Windows seems to be a native Windows app.
Typically I use the activity monitor to analyze the file content. There is always 1 lib at least that a specific framework brings along, even in case of native programs.
When that is not enough, you can also get some cues from the Accessibility Inspector to "guess" what a program uses.